This invention relates to the art of the catalytic cracking of hydrocarbons. In another aspect, the invention relates to reducing the detrimental effects of contaminating deposits on a cracking catalyst. In still another aspect, the invention relates to the passivation of metals on cracking catalysts.
In most conventional catalytic cracking processes in which hydrocarbon feedstocks are cracked to produce light distillates a gradual deterioration of the catalyst occurs. Some of this deterioration is attributable to the deposition on the catalyst of contaminants contained within the feedstock. The deposition of these contaminants, which include nickel, vanadium and iron, tends to adversely affect the cracking process by decreasing conversion of the feedstock to cracked products, decreasing production of gasoline and increasing yields of hydrogen and coke.
It is known in the art that the adverse effects of catalyst contamination can be partially offset by treating the cracking catalyst with passivating agents, for example, antimony and its compounds. Treatment of the cracking catalyst with antimony is extremely desirable in that all four indicia of catalyst deterioration due to deposits of contaminants are improved. Conversion and selectivity to gasoline increase, while hydrogen and coke production decrease. Other passivating agents do not result in improvement in all four indications of undesirable cracking behavior due to deposits of contaminants on the catalyst. In fact, some passivating agents actually worsen one or more of the indicators of undesirable cracking behavior, for example, by decreasing conversion, but are still termed a passivating agent because they improve another of the indicators, for example, by reducing the production of hydrogen.
Cracking catalysts which are resistant to acquiring undesirable cracking behavior when contaminants are deposited thereon from the feedstock are very desirable in that they make possible the economic conversion of poor quality feedstocks to gasoline and other light hydrocarbons. Because poor quality feedstocks are in relative abundance, there is a need for new and improved passivating agents which impart more desirable cracking characteristics to contaminated cracking catalysts. There is also a need for passivating agents which impart to cracking catalysts resistance to becoming adversely affected by contamination from the feedstock. Because of environmental laws which might restrict the use of certain passivating agents, it is also extremely desirable to provide alternative passivating agents so that contaminated oils can continue to be economically cracked.